Solar tides in the equatorial upper thermosphere: A comparison between AE‐E data and the TIGCM for solstice, solar minimum conditions

Abstract

Equatorial thermospheric tidal temperatures and densities inferred from Atmosphere Explorer E (AE‐E) mass spectrometer data are compared with theoretical predictions from the National Center for Atmospheric Research Thermosphere/Ionosphere General Circulation Model (TIGCM) for solar minimum, solstice conditions. The thermospheric diurnal and semidiurnal tides are excited in situ by solar heating and by ion‐neutral momentum coupling. Semidiurnal tides are also generated by upward propagating waves excited by heating in the lower atmosphere. The model calculations include all of these sources. The TIGCM reproduces the gross tidal features observed by the satellite, including the midnight temperature anomaly, and the diurnal phases are in good agreement for the densities of atomic oxygen and molecular nitrogen. However, for the neutral temperature, the predicted phases are 1–2 hours earlier than observed. In addition, the diurnal temperature and density amplitudes predicted by the model are considerably weaker than indicated by the AE‐E measurements. The semidiurnal variations found in the observations agree well with the model for December solstice but not for June. The present results indicate that upward propagating tides from the lower atmosphere are responsible for at least half of the amplitude of the semidiurnal tide in the upper thermosphere.